Table and elevation lock therefor

ABSTRACT

A table capable of having its support surface adjusted to different selected elevations, such as drafting table, which is equipped with an elevation lock mechanism including a pair of rollers normally urged by a spring into engagement with flat opposite side surfaces of a locking bar to anchor that bar, and the support surface to which it is connected, against vertical movement. The rollers are journaled in the openings of a roller support arm assembly which in turn is capable of being pivoted about a line passing through the bar&#39;&#39;s longitudinal mid-plane. By the depression of a foot pedal, the force of the spring upon the roller support arm assembly is relieved, the arm assembly shifts under the influence of gravity into an unlocking position, and the bar along with its connected support surface may be shifted into a different selected elevation where it may again be relocked by simply releasing the pedal.

1.11 3,710,735 [4 1 Jan. 16,1973

[54] TABLE AND ELEVATION LOCK THEREFOR [75] Inventors: James R. Litvinoff, Phillips; David F. Evans; Joseph R. Klug, both of Manitowoc, all of Wis.

[73] Assignee: American Hospital Supply Corporation, Evanston, Ill.

22 Filed: Jan. 4, 1971 21 Appl.No.: 103,469

3,273,517 9/1966 Amthor, Jr. et al. ..108/2 Primary Examiner -Bobby R. Gay

Assistant Examiner-Glenn O. Finch Attorney--Dawson, Tilton, Fallon & Lungmus [5 7 ABSTRACT A table capable of having its support surface adjusted to different selected elevations, such as drafting table, which is equipped with an elevation lock mechanism including a pair of rollers normally urged by a spring into engagement with flat opposite side surfaces of a locking bar to anchor that bar, and the support surface to which it is connected, against vertical movement. The rollers are journaled in the openings of a roller support arm assembly which in turn is capable of being pivoted about a line passing through the bars longitudinal mid-plane. By the depression of a foot pedal, the force of the spring upon the roller support arm assembly is relieved, the arm assembly shifts under the influence of gravity into an unlocking position, and the bar along with its connected support surface may be shifted into a different selected elevation where it may again be re-locked by simply releasing the pedal.

28 Claims, 4 Drawing Figures PATENIEUJAI 16 I975 SHEET 1 [IF 2 :F W F 0 MN E IS V N m A V E I 4 gm MD 5 4 JOSEPH R. KLUG AT T'YS TABLE AND ELEVATION LOCK THEREFOR BACKGROUND Drafting tables, laboratory tables, and a variety of other tables, stands, and the like are often equipped with support surfaces which are capable of being moved into different selected elevations. While counterbalancing means, usually in the form of counterbalancing springs, help to retain such support surfaces at selected elevations, some positive locking mechanism is nevertheless required to prevent unintentional downward movement of such support surfaces when objects are placed thereon or when downward force is otherwise applied thereagainst. Various types of locking mechanisms have been used in the past; however, such devices often slip, chatter, or otherwise malfunction after periods of extended use. Damage to the locking mechanisms is often caused by simply operating the releasing means, usually a foot pedal, too quickly or too far, usually necessitating readjustment, repair, or replacement of elements of the locking mechanism.

SUMMARY The present invention is directed at overcoming the shortcomings of prior elevation lock mechanisms. In particular, it is an object of the invention to provide a mechanism in which a control locking force is exerted to bring smooth locking surfaces into engagement with each other, producing a locking action which will effectively maintain the support surface at a selected elevation (unless excessive downward force is applied) without biting, scoring, notching, or otherwise damaging such surfaces. If an excessive downward force is applied to the support surface, the locking action of the elevation lock mechanism will be overcome without causing damage to the elements of that mechanism.

One aspect of the invention lies in utilizing a pair of parallel and cylindrical rollers, in conjunction with a locking bar having flat opposing surfaces, to lock a table surface at any selected elevation. The rollers are disposed along opposite sides of the bar and are spaced apart a distance slightly greater than the thickness of the bar. A roller support consists primarily of a pair of arms having openings which rotatably receive end portions of the rollers. Such arms are pivotally mounted for movement between an unlocking position wherein at least one of the rollers is disengaged from the bar and a locking position wherein both of the rollers make straight line contacts with the bars opposite side surfaces. In addition, when the rollers are urged into locking engagement with the bar, their end portions make frictional contact with arcuate surface portions of the arms that is, portions of the arms which define portions of the openings in which the ends of the rollers are journaled. Since the rollers are free to rotate at all times except when the bar is firmly locked in place (rotational movement being possible even then if an excessive force is applied to the support surface), renewed or different contact surfaces are provided whenever a height adjustment is made. Because the contacts are along lines or surfaces rather than at points, the possibilities of cutting, notching, or scoring of the parts through the application of locking forces are virtually eliminated. Furthermore, there is no chattering of the parts as the support surface is raised and lowered, and such surface will hold uniformly at any of an infinite number of positions within a predetermined range of movement rather than in a limited number of such positions or in just those positions in which some notching or scoring has occurred.

Other objects and advantages will appear from the specification and drawings.

DRAWINGS FIG. 1 is a side elevational view of a drafting table equipped with the improved elevation lock mechanism, broken lines indicating the relationship of parts when the support surface is in a lowered position;

FIG. 2 is a fragmentary side elevational view of the table with a side panel removed therefrom;

FIG. 3 is a fragmentary and exploded perspective view illustrating details of the elevation lock mechanism;

FIG. 4 is an enlarged and somewhat schematic sectional view illustrating the relationship of parts when locking action occurs.

DESCRIPTION Referring to the drawings FIG. 1 illustrates a drafting table 10 having a table or support surface assembly designated generally by the numeral 11 and a base or supporting assembly designated generally by 12. The support surface assembly 11 is shown in a raised position in solid lines and is presented in a lowered position of adjustment by broken lines. The support surface assembly consists essentially of a table or board 13 mounted upon uprights 14 which are in turn carried by upper and lower parallelogram links 15 and 16. It is to be understood that the uprights and the links to which they are pivotally connected are provided at opposite sides of the unit. At their rear ends, links 15 and 16 are pivotally connected to a frame member 17 of base assembly 12 (FIG. 2). A transverse connecting tube 18 joins links 15 so that the links on opposite sides move in unison. One or more tension springs 20 are disposed within the cavity of the base assembly and, being connected at their lower end to extensions of links 16, exert an upward force upon the parallelogram links to counterbalance the weight of the top assembly 11.

The elevation lock mechanism is designated generally by the numeral 21 and while only one such mechanism appears in the drawings because of the particular views selected, it is to be understood that a pair of such mechanisms are normally provided, one on each side of the base assembly, and are coupled for simultaneous release upon the depression of a single pedal 22 as hereinafter described. Since such mechanisms are identical in structure and operation, only one will be described in detail herein.

Elevation lock mechanism 21 includes a generally vertical locking bar 23 which, as shown most clearly in FIG. 3, is generally rectangular in cross sectional configuration. The bars upper end is welded or otherwise rigidly secured to a forwardly and upwardly extending member 24 which in turn has its upper end pivotally connected to upright 14. Consequently, when the top assembly 11 travels between its raised and lowered positions, the generally vertical locking bar 23 also travels upwardly and downwardly. It will be observed that when the top assembly 11 is in its partly lowered position as shown in FIG. 2, bar 23 is not precisely vertical; however, as the top assembly is shifted upwardly, the bar moves into a more nearly vertical position and, because of the pivoting action of the parallelogram linkage, even assumes a slightly reverse slope (i.e., upwardly and rearwardly) when the top assembly is fully raised. It is intended, however, that the locking bar be maintained in as close as possible to vertical position throughout the entire range of movement of the top assembly.

The flat, parallel, opposing side surfaces 23a and 23b of the locking bar are normally engaged by a pair of rollers 25 and 26, such rollers being generally cylindrical in configuration and having their axes parallel to said surfaces and normal to the axis of the locking bar. The rollers are spaced apart at distance greater than the distance between the bars opposite side surfaces; thus, when a plane passing through the axes of both rollers is disposed normal to the axis of the bar, the bar will be free to shift longitudinally between such rollers.

In the particular illustration given, the ends of the rollers 25a and 260 are journaled in openings 27 provided in the arms 28 and 29 of a roller support assembly 30. Pivot pins 31 project outwardly from points midway between the paired openings 27 thereof and are received within the apertures 32 in the sides 33 of upstanding channel member 34, the sides of such channel also serving to retain rollers 25 and 26 in their journals. Therefore, the arms 28 are supported for pivotal movement about a transverse axis parallel with and equidistant between the axes of rollers 25 and 26.

Channel member 3.4 is rigidly secured to the base assembly by any suitable means. In the form illustrated, one of its sides is welded or otherwise affixed to a frame member 35 and its lower end is secured to frame member 36. It is to be understood, however, that any suitable means for maintaining channel member 34, and hence the pivot axis of arm assembly 30, immovable with respect to the base assembly may be used.

Arms 28 and 29 are provided with end portions 28a and 29a which project away from locking bar 23 and which are provided with notches or recesses 37 along their lower surfaces. Such notches of the parallel arms normally receive the laterally projecting pins 38 of a latch member 39 which, in the embodiment shown, is vertically elongated and is of U-shaped cross sectional configuration. The latch member is attached by means of upstanding hook 40 to the lower end of atension spring 41, the spring having its upper end connected to a suitable bracket 42 within the cavity of the base (FIG. 2). The parts are positioned and arranged so that spring 41 normally exerts an upward force upon the projecting ends of arms 28 and 29, thereby pivoting the arms about the axis of pivots 31 and urging the two rollers 25 and 26 into firm contact with opposite side surfaces 23a and 23b of locking bar 23.

Release of the locking force is achieved simply by lowering the latch member 39 so that the free ends 28a and 29a of the roller support arms drop downwardly under the influence of gravity and swing the rollers 25 and 26 into a position wherein a plane passing through their axes is more nearly normal to the axis of locking bar 23; At least one of the rollers is therefore shifted out of engagement with the locking bar. With the roller support arms having been shifted into unlocking positions, the rollers no longer clamp the upstanding bar and the entire top assembly 11 is therefore free to be moved vertically into a new position of adjustment.

Lowering of the free ends of the roller support arms is achieved by means of pedal 22 which is pivotally carried by support rod 43, the rod being rotatably connected to the base 12 by means of brackets 44. An angular extension 45 of rod 43 has its end connected to upstanding rod 46 which in turn has its upper end affixed to latch member 39. If desired, rod 46 and hook 40 may be formed integrally and may be welded or connected by any other suitable means to latch member 39.

Since depression of pedal 22 simply relieves the upward force exerted by spring 41 upon the arm assembly 30, and since the arms are permitted to drop into unlocking positions of their own weight rather than being pulled downwardly by the releasing means, depression of pedal 22, no matter how forceful or abrupt, cannot damage rollers 25-26 or bar 23. There is no danger that if pedal 22 were depressed beyond a certain point the unlocking force might carry the rollers too far in an un locking direction and might again produce a locking action.

Of particular importance is the fact that the locking surfaces are continually renewable because the locking elements or rollers are free to rotate at any time other than when they are in fully locked positions and, in fact, may even rotate when they are in fully locked positions if an excessive downward force were applied to the top assembly 11. As indicated in FIG. 4, when the parts are in their locking positions rollers 25 and 26 make contact with surfaces 23a and 23b along lines or narrow zones 47 extending horizontally and transversely with respect to the axis of locking bar 23 and longitudinally with respect to the axes of the rollers. At the same time, the rollers are urged outwardly into forceful engagement with arcuate portions 48 of the surfaces of each arm 28 which define portions of the openings 27 in which the ends of the rollers are journaled. Since each of the arms extends in a generally vertical plane, such arcuate surfaces extend in circumferential directions with respect to the ends of the rollers. Here again, since forceful engagement extends along a line or narrow zone rather than at a point, there is no danger that the parts will become notched or scored by reason of the locking force applied by the spring means.

While in the foregoing an embodiment of the invention has been disclosed in considerable detail for purposes of illustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.

We claim:

1. An elevation lock mechanism comprising a locking bar having a pair of opposite sides providing smooth and parallel surfaces; a pair of parallel and cylindrical rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance greater than the distance between said opposite sides; a roller support including a pair of arms having openings rotatably receiving end portions of said rollers; said arms having arcuate surfaces defining circumferential portions of said openings; and means pivotally mounting said arms for movement between an unlocking position wherein at least one of said rollers is disengaged from said bar and a locking position wherein both of said rollers make straight line contact with said opposite side surfaces of said bar and also make frictional contact in directions extending circurn ferentially of said end portions with said arcuate surfaces of said arms.

2. The structure of claim 1 in which spring means are provided for urging said arms into said locking position.

3. The structure of claim 2 in which releasing means are provided for relieving the locking force exertedby said spring means upon said arms.

4. An elevation lock mechanism comprising a locking bar having a pair of opposite sides providing smooth and parallel surfaces; a pair of parallel and cylindrical rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance greater than the distance between said opposite sides; a roller support including a pair of arms having openings rotatably receiving end portions of said rollers; said arms having arcuate surfaces defining circumferential portions of said openings; means pivotally mounting said arms for movement between an unlocking position wherein at least one of said rollers is disengaged from said bar and a locking position wherein both of said rollers make straight line contact with said opposite side surfaces of said bar and also make frictional contact in directions extending circumferentially of said end portions with said arcuate surfaces of said arms; spring means for urging said arms into said locking position; releasing means for relieving.

the locking force exerted by said spring means upon said arms; said arms having parallel end portions projecting away from said locking bar; and a latch member being connected to said spring means and being normally urged thereby into engagement with said end portions of said arms to pivot said arms into said locking position.

5. The structure of claim 4 in which said releasing means are also connected to said latch member for selectively shifting the same out of engagement with said arms for permitting movement of the arms into their unlocking position.

6. The structure of claim 5 in which said locking bar extends in a generally vertical direction and said arms are generally horizontally disposed; said spring means cooperating with said latch member to urge the same in one generally vertical direction and said releasing means being operable to shift said latch member in the opposite direction.

7. The structure of claim 6 in which said latch member is engagable with the undersurfaces of said arms adjacent the said ends: thereof; said spring means urging said latch member u pwardly to engage the undersurfaces of said arms andsaid releasing means being operative to lower said latch member out of such engagement.

8. The structure of claim 7 in which said arms are moved into said unlocking position under the influence of gravity' 9. The structure of claim 7 in which said releasing means includes a foot pedal connected to said latch member.

10. The structure of claim 7 in which said latch member is provided with laterally-projecting pins and said undersurfaces of said arms are notched for releasably receiving said pins.

11. An elevation lock mechanism comprising a locking bar having opposite sides providing a pair of flat, smooth, and parallel surfaces; a pair of parallel rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance slightly greater than the distance between such surfaces; said rollers having their ends rotatably carried by a pair of armspivotal abouta transverse axis which is parallel with said rollers and which is equidistant therebetween; means mounting said bar and arms for relative movement of said bar between said rollers; spring means for pivoting said arms about said transverse axis to urge the cylindrical surfaces of said rollers into engagement with said opposite surfaces of said bar and thereby locking said bar and rollers against relative movement; and releasing means for releasing the force of said spring means upon said arms.

12. The structure of claim 11 in which said rollers have their ends journaled in openings provided in said arms; said ends of said rollers having perimetric portions thereof normally urged by said spring means into frictional contact with said arms along arcuate portions of said openings.

13. The structure of claim 11 in which said mounting means mounts said bar and arms for relative transverse floating movement of said bar between said rollers, whereby, the force exerted by said rollers under the influence of said spring means is equalized against said opposite surfaces of said bar.

1.4. An elevation lock mechanism comprising a locking bar having opposite sides providing a pair of flat, smooth, and parallel surfaces; a pair of parallel rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance slightly greater than the distance between such surfaces; said rollers having their ends rotatably carried by a pair of arms pivotal about a transverse axis which is parallel with said rollers and which is equidistant therebetween; means mounting said bar and arms for relative movement of said bar between said rollers; spring means for pivoting said arms about said transverse axis to urge the cylindrical surfaces of said rollers into engagement with said opposite surfaces of said bar and thereby locking said bar and rollers against relative movement; releasing means for releasing the force of said spring means upon said arms; said rollers having their ends journaled in openings provided in said arms; said ends of said rollers having perimetric portions thereof normally urged by said spring means into frictional contact with said arms along arcuate portions of said openings; said mounting means mounting said bar and arms for relative transverse floating movement of said bar between said rollers, whereby, the force .exerted by said rollers under the influence of said spring means is equalized against said opposite surfaces of said bar; said arms having parallel end portions projecting away from said bar; a latch member being connected to said spring means and normally being urged thereby into engagement with said end portions of said arms to pivot the same about said transverse axis and to lock said rollers and bar against relative movement;

said releasing means also being connected to said latch member for selectively shifting the same out of engagement with said arms.

15. The structure of claim 14 in which said bar extends in a generally vertical direction and said arms are generally horizontally disposed; said spring means cooperating with said latch member to urge the same in one generally vertical direction and said releasing means being operative to shift said latch member in the opposite direction.

16. The structure of claim 15 in which said latch member is engagable with the undersurfaces of said arms adjacent said ends thereof, said spring means urging said latch member upwardly to engage the undersurfaces of said arms and said releasing means being operative to lower said latch member out of such engagement.

17. The structure of claim 16 in which said releasing means includes a foot pedal connected to said latch member.

18. The structure of claim 16 in which said latch member is provided with laterally projecting pins and said undersurfaces of said arms are notched for releasably receiving such pins.

19. In combination, a table top assembly; a table base assembly; connecting means movably supporting said top assembly for movement into different elevations upon said base assembly; and an elevation lock mechanism comprising a locking bar having a pair of opposite sides providing smooth and parallel surfaces; a pair of parallel'and cylindrical rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance greater than the distance between said opposite sides; a roller support including a pairof arms having openings rotatably receiving end portions of said rollers; said arms having arcuate surfaces defining circumferential portions of said openings; and means pivotally mounting said arms for movement between an unlocking position wherein at least one of said rollers is disengaged from said bar and a locking position wherein both of said rollers make straight line contact with opposite side surfaces of said bar and also make frictional contact in directions extending circumferentially of said end portions with said arcuate surfaces of said arms; one of said assemblies being connected to said bar and the other of said assemblies being connected to said roller support, whereby, said top assembly may be releasably locked in any of a number of selected elevations relative to said base assembly.

20. The structure of claim 19 in which spring means is provided for urging said arms into said locking position.

21. In combination, a table top assembly; a table base assembly; connecting means movably supporting said top assembly for movement into different elevations upon said base assembly; and an elevation lock mechanism comprising a locking bar having a pair of opposite sides providing smooth and parallel surfaces; a pair of parallel and cylindrical rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance greater than the distance between said opposite sides; a roller support including a pair of arms having openings rotatably receiving end portions of said rollers; said arms having arcuate surfaces defining circumferential portions of said openings; means pivotally mounting said arms for movement between an unlocking position wherein at least one of said rollers is disengaged from said bar and a locking position wherein both of said rollers make straight line contact with opposite side surfaces of said bar and also make frictional contact in directions extending circumferentially of said end portions with said arcuate surfaces of said arms; one of said assemblies being connected to said bar and the other of said assemblies being connected to said roller support, whereby, said top assembly may be releasably locked in any of a number of selected elevations relative to said base assembly; spring means for urging said arms into said locking position; and releasing means for relieving the locking force exerted by said spring means upon said arms.

22. The structure of claim 21 in which said arms have parallel end portions projecting away from said bar; and a latch member connected to said spring means and normally urged thereby into engagement with said end portions of said arms to pivot said arms into said locking position.

23. The structure of claim 22 in which said releasing means is also connected to said latch member for selectively shifting the same out of engagement with said arms for permitting movement of the arms into their unlocking position.

24. The structure of claim 23 in which said bar extends in a generally vertical direction and said arms are generally horizontally disposed; said spring means cooperating with said latch member to urge the same in one generally vertical direction and said releasing means being operative to shift said latch member in the opposite direction.

25. The structure of claim 24 in which said latch member is engagable with the undersurfaces of said arms adjacent said ends thereof; said spring means urging said latch member upwardly to engage the undersurfaces of said arms and said releasing means being operative to lower said latch member out of such engagement.

26. The structure of claim 25 in which said releasing means includes a foot pedal connected to said latch member.

27. The structure of claim 26 in which said latch member is provided with laterally-projecting pins and said undersurfaces of said arms are notched for releasably receiving said pins.

28. In combination, a table top assembly; a table base assembly; connecting means movably supporting said top assembly for movement into different elevations upon said base assembly; and an elevation lock mechanism comprising a locking bar having a pair of opposite sides providing smooth and parallel surfaces; a pair of parallel and cylindrical rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance greater than the distance between said opposite sides; a roller support including a pair of arms having openings rotatably receiving end portions of said rollers; said arms having arcuate surfaces defining circumferential portions of said openings; and means pivotally mounting said arms for movement between an unlocking position wherein at least one of said rollers is disengaged from said bar whereby, said top assembly may be releasably locked in any of a number of selected elevations relative to said base assembly: said table top assembly being operatively connected to said locking bar and said base assembly being operatively connected to said roller support. 

1. An elevation lock mechanism comprising a locking bar having a pair of opposite sides providing smooth and parallel surfaces; a pair of parallel and cylindrical rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance greater than the distance between said opposite sides; a roller support including a pair of arms having openings rotatably receiving end portions of said rollers; said arms having arcuate surfaces defining circumferential portions of said openings; and means pivotally mounting said arms for movement between an unlocking position wherein at least one of said rollers is disengaged from said bar and a locking position wherein both of said rollers make straight line contact with said opposite side surfaces of said bar and also make frictional contact in directions extending circumferentially of said end portions with said arcuate surfaces of said arms.
 2. The structure of claim 1 in which spring means are provided for urging said arms into said locking position.
 3. The structure of claim 2 in which releasing means are provided for relieving the locking force exerted by said spring means upon said arms.
 4. An elevation lock mechanism comprising a locking bar having a pair of opposite sides providing smooth and parallel surfaces; a pair of parallel and cylindrical rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance greater than the distance between said opposite sides; a roller support including a pair of arms having openings rotatably receiving eNd portions of said rollers; said arms having arcuate surfaces defining circumferential portions of said openings; means pivotally mounting said arms for movement between an unlocking position wherein at least one of said rollers is disengaged from said bar and a locking position wherein both of said rollers make straight line contact with said opposite side surfaces of said bar and also make frictional contact in directions extending circumferentially of said end portions with said arcuate surfaces of said arms; spring means for urging said arms into said locking position; releasing means for relieving the locking force exerted by said spring means upon said arms; said arms having parallel end portions projecting away from said locking bar; and a latch member being connected to said spring means and being normally urged thereby into engagement with said end portions of said arms to pivot said arms into said locking position.
 5. The structure of claim 4 in which said releasing means are also connected to said latch member for selectively shifting the same out of engagement with said arms for permitting movement of the arms into their unlocking position.
 6. The structure of claim 5 in which said locking bar extends in a generally vertical direction and said arms are generally horizontally disposed; said spring means cooperating with said latch member to urge the same in one generally vertical direction and said releasing means being operable to shift said latch member in the opposite direction.
 7. The structure of claim 6 in which said latch member is engagable with the undersurfaces of said arms adjacent the said ends thereof; said spring means urging said latch member upwardly to engage the undersurfaces of said arms and said releasing means being operative to lower said latch member out of such engagement.
 8. The structure of claim 7 in which said arms are moved into said unlocking position under the influence of gravity.
 9. The structure of claim 7 in which said releasing means includes a foot pedal connected to said latch member.
 10. The structure of claim 7 in which said latch member is provided with laterally-projecting pins and said undersurfaces of said arms are notched for releasably receiving said pins.
 11. An elevation lock mechanism comprising a locking bar having opposite sides providing a pair of flat, smooth, and parallel surfaces; a pair of parallel rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance slightly greater than the distance between such surfaces; said rollers having their ends rotatably carried by a pair of arms pivotal about a transverse axis which is parallel with said rollers and which is equidistant therebetween; means mounting said bar and arms for relative movement of said bar between said rollers; spring means for pivoting said arms about said transverse axis to urge the cylindrical surfaces of said rollers into engagement with said opposite surfaces of said bar and thereby locking said bar and rollers against relative movement; and releasing means for releasing the force of said spring means upon said arms.
 12. The structure of claim 11 in which said rollers have their ends journaled in openings provided in said arms; said ends of said rollers having perimetric portions thereof normally urged by said spring means into frictional contact with said arms along arcuate portions of said openings.
 13. The structure of claim 11 in which said mounting means mounts said bar and arms for relative transverse floating movement of said bar between said rollers, whereby, the force exerted by said rollers under the influence of said spring means is equalized against said opposite surfaces of said bar.
 14. An elevation lock mechanism comprising a locking bar having opposite sides providing a pair of flat, smooth, and parallel surfaces; a pair of parallel rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance slightly gReater than the distance between such surfaces; said rollers having their ends rotatably carried by a pair of arms pivotal about a transverse axis which is parallel with said rollers and which is equidistant therebetween; means mounting said bar and arms for relative movement of said bar between said rollers; spring means for pivoting said arms about said transverse axis to urge the cylindrical surfaces of said rollers into engagement with said opposite surfaces of said bar and thereby locking said bar and rollers against relative movement; releasing means for releasing the force of said spring means upon said arms; said rollers having their ends journaled in openings provided in said arms; said ends of said rollers having perimetric portions thereof normally urged by said spring means into frictional contact with said arms along arcuate portions of said openings; said mounting means mounting said bar and arms for relative transverse floating movement of said bar between said rollers, whereby, the force exerted by said rollers under the influence of said spring means is equalized against said opposite surfaces of said bar; said arms having parallel end portions projecting away from said bar; a latch member being connected to said spring means and normally being urged thereby into engagement with said end portions of said arms to pivot the same about said transverse axis and to lock said rollers and bar against relative movement; said releasing means also being connected to said latch member for selectively shifting the same out of engagement with said arms.
 15. The structure of claim 14 in which said bar extends in a generally vertical direction and said arms are generally horizontally disposed; said spring means cooperating with said latch member to urge the same in one generally vertical direction and said releasing means being operative to shift said latch member in the opposite direction.
 16. The structure of claim 15 in which said latch member is engagable with the undersurfaces of said arms adjacent said ends thereof, said spring means urging said latch member upwardly to engage the undersurfaces of said arms and said releasing means being operative to lower said latch member out of such engagement.
 17. The structure of claim 16 in which said releasing means includes a foot pedal connected to said latch member.
 18. The structure of claim 16 in which said latch member is provided with laterally projecting pins and said undersurfaces of said arms are notched for releasably receiving such pins.
 19. In combination, a table top assembly; a table base assembly; connecting means movably supporting said top assembly for movement into different elevations upon said base assembly; and an elevation lock mechanism comprising a locking bar having a pair of opposite sides providing smooth and parallel surfaces; a pair of parallel and cylindrical rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance greater than the distance between said opposite sides; a roller support including a pair of arms having openings rotatably receiving end portions of said rollers; said arms having arcuate surfaces defining circumferential portions of said openings; and means pivotally mounting said arms for movement between an unlocking position wherein at least one of said rollers is disengaged from said bar and a locking position wherein both of said rollers make straight line contact with opposite side surfaces of said bar and also make frictional contact in directions extending circumferentially of said end portions with said arcuate surfaces of said arms; one of said assemblies being connected to said bar and the other of said assemblies being connected to said roller support, whereby, said top assembly may be releasably locked in any of a number of selected elevations relative to said base assembly.
 20. The structure of claim 19 in which spring means is provided for urging said arms into said locking position.
 21. In combInation, a table top assembly; a table base assembly; connecting means movably supporting said top assembly for movement into different elevations upon said base assembly; and an elevation lock mechanism comprising a locking bar having a pair of opposite sides providing smooth and parallel surfaces; a pair of parallel and cylindrical rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance greater than the distance between said opposite sides; a roller support including a pair of arms having openings rotatably receiving end portions of said rollers; said arms having arcuate surfaces defining circumferential portions of said openings; means pivotally mounting said arms for movement between an unlocking position wherein at least one of said rollers is disengaged from said bar and a locking position wherein both of said rollers make straight line contact with opposite side surfaces of said bar and also make frictional contact in directions extending circumferentially of said end portions with said arcuate surfaces of said arms; one of said assemblies being connected to said bar and the other of said assemblies being connected to said roller support, whereby, said top assembly may be releasably locked in any of a number of selected elevations relative to said base assembly; spring means for urging said arms into said locking position; and releasing means for relieving the locking force exerted by said spring means upon said arms.
 22. The structure of claim 21 in which said arms have parallel end portions projecting away from said bar; and a latch member connected to said spring means and normally urged thereby into engagement with said end portions of said arms to pivot said arms into said locking position.
 23. The structure of claim 22 in which said releasing means is also connected to said latch member for selectively shifting the same out of engagement with said arms for permitting movement of the arms into their unlocking position.
 24. The structure of claim 23 in which said bar extends in a generally vertical direction and said arms are generally horizontally disposed; said spring means cooperating with said latch member to urge the same in one generally vertical direction and said releasing means being operative to shift said latch member in the opposite direction.
 25. The structure of claim 24 in which said latch member is engagable with the undersurfaces of said arms adjacent said ends thereof; said spring means urging said latch member upwardly to engage the undersurfaces of said arms and said releasing means being operative to lower said latch member out of such engagement.
 26. The structure of claim 25 in which said releasing means includes a foot pedal connected to said latch member.
 27. The structure of claim 26 in which said latch member is provided with laterally-projecting pins and said undersurfaces of said arms are notched for releasably receiving said pins.
 28. In combination, a table top assembly; a table base assembly; connecting means movably supporting said top assembly for movement into different elevations upon said base assembly; and an elevation lock mechanism comprising a locking bar having a pair of opposite sides providing smooth and parallel surfaces; a pair of parallel and cylindrical rollers along said opposite sides having their axes parallel to said surfaces and being spaced apart a distance greater than the distance between said opposite sides; a roller support including a pair of arms having openings rotatably receiving end portions of said rollers; said arms having arcuate surfaces defining circumferential portions of said openings; and means pivotally mounting said arms for movement between an unlocking position wherein at least one of said rollers is disengaged from said bar and a locking position wherein both of said rollers make straight line contact with opposite side surfaces of said bar and also make frictional contact in directions extending circumferentially of said end pOrtions with said arcuate surfaces of said arms; one of said assemblies being connected to said bar and the other of said assemblies being connected to said roller support, whereby, said top assembly may be releasably locked in any of a number of selected elevations relative to said base assembly: said table top assembly being operatively connected to said locking bar and said base assembly being operatively connected to said roller support. 